I have a small project in which I switched from standard values to java.util.Optional. Now any validation results in NullPointerExceptions in ValueContext.appendNode.
When redesigning the objects, I changed them from interfaces to abstract classes, but that should not inhibit validation. All fields are wrapped in Optional before returning, but are stored directly. Both field and method annotations lead to NullPointerExceptions. In fact, when changing one of the getters to return the field directly, with Optional wrapping, it still leads to NullPointerException.
I will try to track it down further. But I can't think of anything else I modified that could explain this.